UPSC 2013 CDS 2 Math Paper

Difference between the speeds = 15 kmph – 10 kmph = 5 kmph
Difference between the time =120 min
Now, 5 kmph takes time = 120 min
1 kmph takes time =

120

5

=24 min
So, 24 min are taken at the speed of 1 kmph
For 60 min, speed
=

60

24

=2.5kmph
Therefore, the speed of cyclist should be 12.5 kmph.